INT 67H 4300H: Open EMM Handle and Allocate Memory

                                                     Compatibility: EMS 3.2+ 
 Expects: AX    4300H
          BX    number of pages requested (16K units)
          ──────────────────────────────────────────────────────────────────
 Returns: AH    EMM status (0=successful)
          DX    EMM handle of allocated memory (if successful)
          ──────────────────────────────────────────────────────────────────
    Info: Allocates EMS memory.

          The handle returned in DX is used in subsequent calls to map the
          EMS into the page frame and other operations.

   Notes: Use INT 67H 4200H to see how much EMS is available.

See Also: INT 67H: EMM Services
          Extended Memory Specification (XMS)
          Interrupts and BIOS Services
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